Content data distribution terminal and content data distribution system

A content distribution system having a content distribution server distributing encrypted content data resulting from encryption of content data with content key data and first encrypted content key data resulting from encryption of the content key data with user key data, and a content distribution terminal recording the encrypted content data and the first encrypted content key data on a recordable medium, wherein

• the content distribution terminal comprises:
• a user key data generation unit generating new user key data representing a new version of the user key data;
• a user key update unit capturing, from the recordable medium, already-recorded user key data representing the user key data that has already been recorded on the recordable medium, and ordering the user key data generation unit to generate the new user key data when a predetermined situation is identified in the already-recorded user key data to execute an update procedure for the user key data;
• an erase control unit erasing, when a predetermined situation is identified in the already-recorded user key data, the first encrypted content key data that is encrypted with the already-recorded user key data and stored in the recordable medium;
• an encryption/decryption unit decrypting, with terminal-unique key, second encrypted content key data resulting from encryption of the content key data with different terminal-unique keys for different terminals, encrypting again content key data resulting from decryption of the second encrypted content key data with the new user key data to generate the first encrypted content key data, and encrypting the content data with the content key data to generate the encrypted content data;
• and
• a write control unit writing the first encrypted content key data and the encrypted content data generated by the encryption/decryption unit to the recordable medium.